1. Field of the Invention
This invention relates to a hologram recording medium and a hologram recording apparatus and a hologram recording method by which sound information of voice, music or the like, image information of still pictures or moving pictures, or information of a text file or the like is recorded as an element hologram after it is two-dimensionally modulated.
2. Description of the Related Art
Referring to, for instance, to Japanese Patent No. 2833975, where information is recorded on a sheet-like recording medium, it typically assumes a one-dimensional code or a two-dimensional code represented by a bar code, a QR code, and a dot code. However, where information is recorded in a one- or two-dimensional code, the amount of information which can be recorded per unit area of a recording medium is as low as several tens to several kilobytes. This is because the recording medium has a physical limit to the recording resolution in variable-density printing of a mere image.
Also a hologram recording medium on which various data are recorded as interference fringes of object light and reference light is known as one of sheet-like recording media. Also it is known that the hologram recording medium allows recording of a very high density and hence of a very large amount of information. Therefore, the hologram recording medium is expected as a very useful storage medium of a large capacity suitable for storage of, for example, computer data and AV (Audio-Visual) content data such as audio data and video data.
In order to record data on a hologram recording medium, the data are converted into two-dimensional page data of an image. Then, the image data are displayed on a liquid crystal panel or the like, and light which passes through the liquid crystal panel is irradiated as object light on the hologram recording medium so as to make an image of the two-dimensional page data. In addition, reference light is irradiated in a predetermined angle to the hologram recording medium. Thereupon, interference fringes produced by the object light and the reference light are recorded as an element hologram in the form of dots or rectangles. In short, one element hologram is a record of one two-dimensional page data.